1. Field of the Invention
The present invention relates to cement products containing magnesium oxide and aluminum phosphate, and more particularly to rapid-setting compositions and high-compressive-strength concrete-like products formed therefrom.
2. Description of the Prior Art
Cements are particulate materials that set up and harden to strong, dense monolithic solids upon being mixed with a liquid and allowed to stand. Cements find utility in many areas of commerce, especially in the construction industry, where they are often used in conjunction with various aggregate materials to form such articles as concrete slabs, etc. Cements are also used for highway construction, and in highway patching operations. For highway patching, quick-setting cements, or, more specifically, quick-setting compositions formed by mixing the cements with liquids, are required so that road-closing times can be kept to a minimum. Rapid-setting compositions are also advantageous for masonry work, home repairing, making building panels and self-levelling floors, setting fence posts, etc.
U.S. Pat. No. 4,394,174 describes cement products, and rapid-setting compositions made therefrom, containing magnesium oxide and aluminum phosphate, which compositions are workable for a length of time, i.e., at least ten minutes, sufficient, for example, to allow them to be comfortably mixed, placed in a hole to be patched, spread, and trowelled. Thereafter the compositions are said to harden quickly, e.g., within one hour, at which time, for example, vehicular traffic can be allowed to pass over a patch. The required working time is achieved by proper control of the concentrations of the magnesium oxide and aluminum phosphate and the amount of inert aggregate also present, and of the surface area and particle size of the magnesium oxide in a manner such that the reaction exotherm is reached after a ten-minute interval.
The repairing or patching of cracks, holes, and spalled areas with rapid-setting phosphate cements usually is performed in weight-bearing surfaces such as highways, airfield pavements, driveways, bridgedecks, and the like. Inasmuch as the patch has to support vehicular traffic, and should be durable, the hardened product should have a high compressive strength.